Tissue interaction in the scaleless mutant and the use of scaleless as an ectodermal marker in studies of normal limb differentiation

✍ Scribed by Goetinck, Paul F. ;Abbott, Ursula K.

• Publisher: John Wiley and Sons
• Year: 1963
• Tongue: English
• Weight: 1012 KB
• Volume: 154
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1401540103

✦ Synopsis

Recently considerable attention has been directed towards the role of the apical ectodermal ridge (AER) in the proximo-distal differentiation of limb parts. In the absence of the AER, which caps the distal tip of early limb buds, no terminal structures develop (Saunders, '48; Amprino and Camosso, '55a, b; Zwilling, '49, '55; Hampk, '56, '59). Implantation of proximal leg mesoderm i n direct contact with the AER of the wing bud results in the formation of distal elements with leg characteristics (Saunders, Gasseling and Cairns, '55, '59; Saunders, Cairns and Gasseling, '57). Grafts of an AER on each lateral surface of a previously denuded limb mesoblast results in the development of duplicated limbs (Zwilling, '56a). In addition, a more extensive AER covers the distal part of both anterior and posterior limb buds in several polydactylous mutants (Zwilling and Hansborough, '56; Abbott, Taylor and Abplanalp, '60; Goetinck and Abbott) (in preparation) and is reduced or absent in hypodactylous mutants (Zwilling, '49, '56b). Because of these experimental results and observations, the AER has been considered as an inductor of limb outgrowth.

While Amprino and Camosso ('55a, b) found that no distal outgrowth occurred after excision of the AER, they reported a variable amount of outgrowth if a few cell layers of underlying mesoderm were removed together with the ectoderm. These authors proposed that the amount of outgrowth obtained is inversely proportional to the amount of cell degeneration in the distal undetermined mesoderm, possibly as a consequence of its exposure to amniotic fluid. Accordingly. this group does not believe that the AER has a n inductive role in limb differentiation (Amprino and Camosso, '55a, b, '59a, b; Barasa, '59, '60).

Bell ('58) and Bell, Kaighn and Fessenden ('59) reported that young limb buds deprived of their ectoderm by means of ultrasound may form terminal limb parts. They observed that the basement membrane breaks down soon after irradiated limb buds are transplanted either to the flank or the coelomic cavity and suggested that the absence of a basement membrane may be a prerequisite for the formation of terminal structures i n an ectodermless limb bud.

More recently, Bell, Saunders and Zwilling ('59) and Zwilling, Saunders and Gasseling ('60) reported that distal limb parts occasionally form when limb buds deprived of ectoderm by use of the chelating compound ethylenediaminetetraacetate (EDTA) are transplanted to the chorioallantoic membrane. However, in these cases the distal outgrowth has been associated with the presence of a refractile or shiny layer on the denuded mesoblast. In their latest joint publication (Bell, Gasseling, Saunders and Zwilling ('62), the refractile layer was established as ectodermal in origin and the authors agreed that no distal outgrowth occurred when all the ectoderm was removed with EDTA. However, they also reported that among 68 mesoblasts denuded of ectoderm after ultrasonation two or possibly three developed distal structures when grafted. These mesoblasts had been classified as being completely free of ectoderm at the time of their transplantation.